After dragging his feet on the matter for almost two weeks, Chief Executive Leung Chun-ying has finally agreed to give a full and open account in Legco of the illegal structures found at his properties on The Peak.

A political scientist said Leung had no other option, as he had to secure his allies' support in the face not only of next week's push in Legco for a vote of no confidence in him, but a special investigation and a move by pan-democrats to impeach him.

Leung yesterday responded to an invitation from Legco's house committee, saying he would "welcome the opportunities" to answer members' questions and would contact the council's secretariat to agree on a "mutually convenient time".

Committee chairman Andrew Leung Kwan-yuen said a meeting would likely be held before December 17. He was unsure whether Leung wanted the session before Wednesday's vote on a motion of no confidence.

The chief executive is expected to face questions that he failed to address in a 14-page statement issued on November 23, the first detailed account since the illegal structures were reported five months ago.

A key question is why he chose not to disclose the illegal extension in the basement of his house at 4 Peel Rise on The Peak when he showed reporters around the property in June.

Although he was made aware that the extension was not legal as early as last year, Leung disclosed it only in last month's statement, drawing criticism that he had "cheated" in the chief executive election by attacking rival Henry Tang Ying-yen for building a much bigger illegal basement at Tang's Kowloon Tong house.

The Buildings Department told Leung on Monday to remove the illegal extension.

The Liberal Party's James Tien Pei-chun, who earlier said the party might support a vote of no confidence, urged Leung to attend the question-and-answer session before the no-confidence motion was proposed.

Acting Democratic Party chairwoman Emily Lau Wai-hing said she was "fed up" with Leung, while lawmaker "Long Hair" Leung Kwok-hung, of the League of Social Democrats, said attempts to seek Leung's impeachment would continue.

Dr Li Pang-kwong, a political scientist at Lingnan University, said Leung had no choice but to give a full account in Legco in order to secure support from the pro-establishment camp.

"The public has already formed their view of Leung's handling of the illegal structure saga," said Li. "Attending a Legco session is merely a move to relieve the pressure on pro-establishment lawmakers so that they will not support the motion of no confidence."

Outstanding questions over structures in the properties of Leung Chun-ying

1. Does Leung Chun-ying have an illegal basement in the Stanley house he owns and moved out of in 1999?

2. Why did Leung not reveal, when he showed reporters illegal structures in his Peak houses in June, an extension in the basement of No 4 Peel Rise that he said he discovered in October last year?

3. Were Buildings Department officers aware of the extension in June when they noticed irregularities in a brick wall there? Did their superiors instruct them not to pursue the matter?

4. Why did the department withhold its findings concerning irregularities in the wall when the Apple Daily asked in June about the possible existence of an illegal room? Why did it also fail to mention the wall when detailing other illegal structures in press releases?

5. Did Carrie Lam Cheng Yuet-ngor, then secretary for development, interfere in the department's investigation?

6. Why did four professionals appointed by Leung to check his houses in June fail to bring up the basement issue?

7. Will the department investigate the developer and architect if the basement is proved to have been built before the house was sold to Leung?